The TARDIS is destroyed when an immense and mysterious gravitational force drags it to the planet Frontios. The Doctor, Tegan and Turlough find themselves stranded on a small Earth colony that is experiencing its own problems. Colonists are being sucked into the planets "hungry earth". Never to be seen again. What horror lies beneath the surface of Frontios? Who is the Gravis and what does he want? And what will the Doctor do without the TARDIS?